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Cheap knock box


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From what Ive read a cheap headphone amp and stock knock sensor will give a pretty good indication of knock but would it work throwing in a pot/s that would filter either side 5-7KHZ or a 6khz slider like a graphic equalizer job just to boost the relevant frequencies to make it easier to hear? or am I way off track? Was thinking of hard wiring a cheap internally powered headphone amp along with the stock shielded cable and knock sensor to save me borrowing the early gen knocklink Ive been using.

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Well aware of his FB movements thats what got me thinking again. Headphone amp costs $25 and if i can get it to filter like I think it should then Ill be sailing at half the money with a ****load less unwanted noise.

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I made a really cheap setup with just a jaycar amplifier kit wired to the stock knock sensor which was adequate but not great. Was basically a copy of the early, analogue knockblock.

It works alright but I had also thought about adding better filtering to it. I'm looking into some bandpass filter designs based around op-amps. Texas instruments have some handy software for developing your filter circuits too.

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I was looking at something simple like that but thought adding a filter would be mint. Optical made a 2 pole setup or something didnt he? Rac is sweet with me using his old knocklink but feel like a dick borrowing it all the time.

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Just build something cheap and basic as a starting point then add to it if you feel the need to improve it.

Yeah from memory Optical used some form of Chebyshev or Butterworth filter? Although that's where I like the Texas instruments free software as you can change from one topography to the next by just selecting a different box and it does all the maths for you.

If you get really keen, look up the Texas instruments chip TPIC8101. I'm pretty sure that's the basis of every digital knock device. But it only outputs a pure digital on/off signal or a 0-5v analogue signal to feed a gauge. For audio, you still need to separate the input signal and process it separately.

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http://www.ti.com/tool/filterpro

Looks like I need to update my software as it appears that they've made some useful improvements.

My advice would be to not try to filter it too much, as your ears are still going be a better filter. And using that software it's far too easy for the required design to blow out and become massive to try match unreasonable targets. But it is very easy to use.

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My knock amp was tuneable two-pole high pass and low filters in series and a gain stage.

Here's some frequency analysis from a recording I made like 6 years ago.. Knock frequencies span the band of about 5 to 7khz which matches the theory. The passband width and 3db frequencies were tuneable though.

I lent mine to RAC about 3 years ago and havent seen it since lol, should ask if he still has it...

8-1.jpg

3.jpg

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Not sure if he does Ive only ever seen his old school knock link thats locked at 6khz and run it with a 7A/H SLA and headphones. I dont really want to finetune with it more just see if it has knock on current timing while I hash the fuelling into shape so I can get an idea of egbp and decide what Im doing turbinewise before I get it tuned again.

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